The subject invention relates to a heavy vehicle transmission auxiliary gear box with a power cylinder that uses housing structure other than the piston as a stop.
Heavy vehicles generally utilize transmissions to achieve selected speeds between an engine and an output shaft. A typical transmission includes a main gear box and an auxiliary gear box. The main gear box may includes five gear ranges that may be selected by a vehicle operator. The auxiliary gear box may include a splitter gear box, a range gear box, or both.
The auxiliary gear box of the typical multi-speed transmission may be actuated automatically based upon system conditions or may be actuated by an operator switch. Range or splitter gear changes in the auxiliary gear box are typically driven by a power cylinder. The power cylinder includes a piston driven by a fluid, such as air. The fluid actuates the piston and drives a collar to select a particular output from the auxiliary gear box. The collar engages gears. In conventional auxiliary gear boxes, the piston directly contacts a housing to define an end of a travel stroke of the piston. To move the collar and engage the gears the piston must be driven with high force. Thus, when the piston directly contacts the housing, the piston realizes severe mechanical forces that tend to degrade the physical integrity of the piston.
It would be desirable to have freedom in the selection of materials for the piston. However, to date, materials must be used that allow the piston to provide the stop at the end of the travel stroke.
In a disclosed embodiment, a power cylinder for an auxiliary gear box has a stop structure that does not utilize the piston. A disclosed transmission assembly includes a multi-speed transmission main gear box and an auxiliary gear box coupled to the main gear box. The transmission assembly further includes a power cylinder having a piston housing disposed in the auxiliary gear box. The piston housing defines an internal fluid chamber. A piston shaft extends between proximate and distal ends and is driven between a first position and a second position to effect the shift in the auxiliary gear box. The proximate end of the shaft extends into the internal fluid chamber defined by the piston housing. The distal end of the shaft extends outwardly from the piston housing to a yoke element coupled to the shaft. The yoke element, through interconnection with a collar, selectively engages gears to achieve a desired shift in the auxiliary gear box. In the disclosed embodiment, the auxiliary gear box is a splitter gear box.
The transmission assembly further includes a piston disposed on the proximate end of the shaft. The piston is disposed in the internal fluid chamber to move the shaft and the yoke element between the first position and the second position. The subject invention includes at least one shoulder element extending outwardly from at least one of the ends of the shaft. The shoulder element prevents direct facial contact between the piston and the piston housing when the shaft and the yoke element are actuated between the first and second positions to engage the auxiliary gear box. Preferably, two such shoulder elements define two end of travel stops.
Accordingly, by incorporating at least one shoulder element, the subject invention provides a transmission assembly that prevents the piston from mechanically stopping against the piston housing of the auxiliary gear box. As such, there is greater freedom in the selection of materials for the piston because these materials are not required to withstand impact with the piston housing upon actuation between the first and second positions.